This invention relates to a control system for a battery hybrid system, in which two types of batteries having different characteristics are used as power sources for an electromobile.
In most electromobiles, a lead battery has hitherto been used as a power source. This is because a lead battery is comparatively inexpensive and which is capable of discharging a large amount of current for a short period of time, upon acceleration of a electromobile. The lead battery, however, presents insufficiently high energy density (Wh/kg) to give an acceptably large mileage range to an electromobile. The five-hour term dicharge capacity of the lead battery, in general, ranges from 40 to 50 Wh/kg. An electromobile is therefore short in a possible mileage range, as compared with a gasoline motor vehicle of the same class, and this has been an obstacle in the practical use of the electromobile. In this connection, if the weight of the battery is increased for increasing a weight ratio of the battery to the vehicle, then the possible mileage range of the electromobile could be extended. This, however, results in the increase in the weight of an electromobile itself, thereby lowering the loading capability as well as lowering the performance of the electromobile.
On the other hand, the five-hour-term discharge capacity of a zinc-air battery or an iron-air battery ranges from 80 to 130 Wh/kg, which is twice as high as that of the lead battery. Such a battery, however, is not suited for an electromobile, because of its inability to discharge a large amount of current.